Poly(hexamethylene biguanide): an efficient pH-tolerant and salt-intensive flocculant in the removal of anionic dyes from wastewater

Poly(hexamethylene biguanide) (PHMB) has been extensively studied as an antiseptic and a disinfectant for various areas. However, little attention has been paid to the flocculation performance of PHMB as a cationic polyelectrolyte. The present manuscript investigates the applicability of PHMB as a cationic flocculant for removal of anionic dyes from aqueous solution. It was found that the optimal dosage of 50 ~ 70 mg/L PHBM can effectively remove two model anionic dyes over a wide range of pH value with both rather higher color removal efficiency and lower turbidity. The effect of pH value on the flocculation performance of PHMB mainly lies in the lower dosage (< 60 mg/L), whereas it does not affect the higher dosage of PHMB (> 60 mg/L), suggesting that PHMB is pH-tolerant in the removal of anionic dyes at higher dosage. More interestingly, the addition of inorganic salts was found to enhance the flocculation performance of PHMB, particularly sodium chloride and sodium sulphate, which indicates that the flocculation performance of PHMB increases with increasing ionic strength, i.e., salt-intensive effect. Compared to traditional polymeric flocculants, the present study shows that PHMB has an excellent and comparable flocculation performance in the removal of anionic dyes from aqueous solution, which may extend the application of PHMB in the treatment of dye wastewater. Graphical abstract: [Figure not available: see fulltext.]PHMB used as flocculant for decolorization of dyeing wastewater.